1. Field of the Invention
The present invention relates to a fuel injection device constituting a common rail type fuel injection system of an engine and to an adjustment method thereof. More particularly the invention relates to a fuel injection device for detecting a fuel injection pressure in the system and to an adjustment method thereof.
2. Description of Related Art
Such a device has been known, for example, as described in Patent Document 1 (JP-A-H10-220272). In the common rail type fuel injection system having the fuel injection device, fuel pumped by a fuel pump is accumulated by a common rail in a high-pressure state. The accumulated high-pressure fuel is supplied to respective injectors of cylinders via pipes (high-pressure fuel passages) provided to the respective cylinders. The common rail is provided with a pressure sensor (rail pressure sensor). This system is configured to control driving of various components constituting a fuel supply system by use of the above-mentioned fuel injection device based on an output from the rail pressure sensor.
In recent years, a diesel engine or the like for a vehicle has employed the so-called multiple injection system that performs sub-injection to inject fuel of a smaller quantity than that of main injection before or after the main injection, which generates output torque, in one combustion cycle. For example, noise caused at the time of fuel combustion or an increase in quantity of NOx emission now becomes problematic. In order to improve the current situation, pre-injection or pilot injection is performed as a small quantity of injection before the main injection. In some cases, also after the main injection, after-injection (whose timing is close to that of the main injection) is performed for the purpose of activation of diffusion combustion or decreasing of the quantity of PM (particulate matter) emission. Alternatively, post-injection (whose timing is very late from that of the main injection) is performed for the purpose of raising of an exhaust temperature or activation of a catalyst by supply of a reducing component or the like. The recent engine control involves supplying fuel to the engine in an injection mode (in an injection pattern) that is more appropriate to each of various conditions using one or any combination of various kinds of injections as described above.
The inventors have confirmed that in this case, that is, in the above-mentioned multiple injection, these stages are performed continuously at short intervals, which may lead to a large control error with respect to a target engine operation state as compared to the case of single injection. Specifically, each of injection operations which are continuously performed (in particular sub-injection operations for injecting fuel of a small quantity, other than the main injection operation) is subject to various influences from other injection operations performed before or after the injection operation thereof.
However, the conventional device such as the device disclosed in the above Patent Document 1 has a difficulty in sensing injection characteristics associated with the multiple injection (a plurality of times of continuous injection operations in one combustion cycle) with high accuracy, and more specifically, a pressure fluctuation (waving characteristics) caused by predetermined injection of a multiple injection pattern.